Alkylene glycols, in particular monoalkylene glycols, are of established commercial interest. For example, monoalkylene glycols are being used in anti-freeze compositions, as solvents and as base materials in the production of polyethylene terephthalates e.g. for fibres or bottles.
The production of alkylene glycols by hydrolysis of alkylene oxides is known. It is performed either by liquid phase hydration with an excess amount of water, e.g. of 20 to 25 moles of water per mole of alkylene oxide, or by hydration in a heterogeneous system. The reaction is deemed to be a nucleophilic substitution reaction, whereby opening of the alkylene oxide ring occurs, water acting as the nucleophile. Because the primarily formed monoalkylene glycol likewise acts as nucleophile, as a rule a mixture of monoalkylene glycol, dialkylene glycol and higher alkylene glycols is formed. In order to increase the selectivity to monoalkylene glycols, it is necessary to suppress the secondary reaction between the primary product and alkylene oxide, which competes with the hydrolysis of alkylene oxide.
One effective means for suppressing the secondary reaction is to increase the relative amount of water present in the reaction mixture. Although the selectivity with respect to the monoalkylene glycol is thus improved, a problem is created in that for the recovery of the monoalkylene glycol from the reaction mixture large amounts of water have to be removed, which in turn involves large energy expenditure and is economically unattractive.
Considerable efforts have been made to find alternatives for increasing the selectivity of the process with respect to the monoalkylene glycols, without having to use a large excess of water. Usually, these efforts have focused on the selection of more active hydration catalysts and there are many publications, in which results obtained with various types of catalysts are disclosed.
Both acid and alkaline hydration catalysts have been investigated, whereby it would appear that the use of acid catalysts enhances the reaction rate without significantly affecting the selectivity, whereas by using alkaline catalysts generally lower selectivities with respect to the monoalkylene glycol are obtained.
High conversions, good selectivity and a low water/alkylene oxide ratio can be obtained with the process, disclosed in EP-A-156.449. According to this document, the hydrolysis of alkylene oxides is carried out in the presence of a selectivity-enhancing metalate anion-containing material, preferably a solid having electropositive complexing sites having affinity for the metalate anions. The said solid is preferably an anion exchange resin, the metalate anions are specified as molybdate, tungstate, metavanadate, hydrogenpyrovanadate and pyrovanadate anions. A complication of this process is that the alkylene glycol-containing product stream also comprises a substantial amount of metalate anions, displaced from the electropositive complexing sites of the solid metalate anion containing material. In order to reduce the amount of metalate anions in the alkylene glycol product stream, this stream is contacted with a solid having electropositive complexing sites associated with anions which are replaceable by the said metalate anions.
It has been proposed to simplify the product recovery procedure by using water-insoluble vanadate and molybdate salts. However, with these metalate anion salts the obtained selectivities are significantly lower than with the water-soluble metalates.
In JP-A-57-139026 there is disclosed a method for reacting alkylene oxide with water in the presence of a halogen type anion exchange resin and in the co-presence of carbon dioxide.
In RU-C-2001901 it is pointed out that the former disclosure has the disadvantage of the formation of carbonates in the reaction mixture which are difficult to separate from the glycols on account of the closeness of their boiling points. This patent publication discloses as its invention the performance of the alkylene oxide hydrating reaction in one or a sequence of `extrusion reactor(s)` (continuous reaction), in the presence of `anionite` (anion exchange resin of the quaternary ammonium type) in bicarbonate form and carbon dioxide. The essential difference with the former, Japanese, patent publication appears to be the use of the bicarbonate form of the anion exchanger instead of the halogen form thereof. And yet, the Russian patent does not dispense with the addition of carbon dioxide to the feed.
According to WO 95/20559, the presence of carbon dioxide in the feed is detrimental to the catalytic effect of bicarbonate-exchanged resins of the quaternary ammonium type. In this document there is disclosed a process for the preparation of alkylene glycols wherein an alkylene oxide is reacted with water in the presence of a catalyst composition comprising a solid material having one or more electropositive sites, which are coordinated with one or more anions other than metalate or halogen anions, with the proviso that when the solid material is an anionic exchange resin of the quaternary ammonium type and the anion is bicarbonate the process is performed in the substantial absence of carbon dioxide.
A drawback shared by the conventional anionic exchange resins which are based on purely organic polymers is their limited tolerance to heat. In practicing the process of alkylene oxide hydrolysis according to WO 95/20559 with catalyst compositions based on conventional purely organic quaternary ammonium ion exchangers it has been unexpectedly found, that under severe reaction conditions (high temperature and/or long service) the selectivity of the conventional resin-based catalysts tends to deteriorate strongly while their activity is even enhanced.
Anion exchanging polymeric organosiloxane ammonium salts have been known for some time, but their use as carriers in the instant process has never been contemplated before.
In EP-B 0 065 643 (corresponding to U.S. Pat. No. 4,410,669) polymeric ammonium compounds with a silica type backbone are disclosed, comprising units of the general formula (III) ##STR2## in which R.sup.1 and R.sup.2 represent a group of the general formula (II) ##STR3## in which R.sup.5 is linear or branched alkylene having 1 to 10 C atoms, cycloalkylene having 5 to 8 C atoms, ##STR4## in which n is a number from 1 to 6 and indicates the number of nitrogen-terminated methylene groups, and R.sup.1 and R.sup.2 can be the same or different, and the free valencies of the oxygen atoms are saturated either by silicon atoms of further groups of the formula (II) and/or by crosslinking bridge members of the formula: ##STR5## in which R' is methyl or ethyl and the ratio of the silicon atoms in (II) to the bridge atoms silicon, titanium and aluminum is 1:0 to 1:10,
R.sup.3 and R.sup.4 can have the same scope of meaning as R.sup.1 and R.sup.2 or represent hydrogen, a linear or branched alkyl containing 1 to 20 C atoms, cycloalkyl containing 5 to 8 C atoms or the benzyl group and PA1 R.sup.3 and R.sup.4 can be identical or different and be identical or different to R.sup.1 and/or R.sup.2 PA1 X represents an inorganic or organic, 1- to 3-valent anion of an inorganic or organic protonic acid which forms stable salts with amine bases and x is a number from 1 to 3.
In EP-B 0 065 643 it is also indicated in general terms, that the polymeric organosiloxane ammonium salts are useful as ion exchangers, catalytic carriers or active substance carriers.
In EP-B 0 327 796 (corresponding to U.S. Pat. No. 5,130,396) a method is disclosed for preparing the above organosiloxane amine compounds in spherical form.
In EP-A 0 491 144 (corresponding to U.S. Pat. No. 5,286,885) there are disclosed polymeric organosiloxane amine compounds, having units as in the formula (III) above with the proviso that X is an anion of a monooxo acid, an isopolyoxo acid or a heteropolyoxo acid of the elements vanadium, niobium, tantalum, molybdenum to tungsten. The use of these compounds as catalysts in oxidation reactions whereby peroxo compounds are involved is also disclosed.